I have a problem that I thought I'd fixed about 4 times but it keeps
recurring and is making me quite narked.

When it rains a steady stream of water falls through the air and lands on
the soil about 8in from the wall. The source is a gap in the guttering. The
gap is where 2 adjacent pieces of standard plastic half-pipe meet (not at
right-angles, but "in-line" along the top of a straight stretch of wall).
The pieces don't join directly but both sit on and clip on to a very short
piece of half-pipe which acts as a sort of "junction" piece. (In fact the
junction contains a descender pipe.)

When the gap appears, it looks like one of the long pieces has "drifted
away" horizontally from from the junction piece. With quite a bit of effort
and grunting, I pull it back horizontally towards the junction, where it
seems quite happy to sit (and I even clip it in). But after a while the long
piece drifts away again! How can this happen? I have to exert and grunt
quite a lot to get the piece back in, so what force can take it out again?
Immediately after I've put it back, there seems to be no "spring" action
that wants to take it out again - it seems to come out slowly over time.

Possible bodge solutions include aralditing or screwing the drifting piece
to the junction, perhaps? And why does it happen?

TIA
Cheers
Richard